290 Journal of Agricultural Research voi. iv, no. 4 



gium. They then come to rest, undergo metamorphosis, and emerge 

 as more or less bean-shaped, biciliated zoospores for a second and more 

 prolonged period of motility. This group presents a pronounced condition 

 of diplanetism. 



The second group, on the other hand, comprises Achlya and Apha- 

 nomyces, forms that present a condition of what may be called "reduced 

 diplanetism." Here the first swarm period is reduced to a simple migra- 

 tion from the sporangium. It occurs after the spores are cleaved and is 

 followed by metamorphosis from which the zoospores emerge, as in the 

 first group, for a prolonged period of motility. 



The fungus under consideration seems to present a third and hitherto 

 undescribed type of diplanetism, in which the first motile period consists 

 in the migration of the entire uncleaved sporangium and its contents 

 from the presporangium. This type of egress is new. In all related 

 forms previously described the spores are differentiated before migra- 

 tion. The distinction seems sufficiently important to justify its recog- 

 nition as of generic rank. The uncleaved protoplasm rather than the 

 dififerentiated spore migrates. The process of metamorphosis is elimi- 

 nated and the spores that arise from cleavage have the form characteristic 

 of the second motile period in the other genera mentioned. 



The tendency in the series outlined has been toward monoplanetism, 

 but it hardly seems probable that such a condition has arisen in this 

 manner, since Pythiopsis, the monoplanetic genus of the subdivision, has 

 eliminated metamorphosis and the second motile period rather than the 

 first, giving the entire interval of locomotion to its more or less egg-shaped 

 spores, the form type characteristic of the first motile period of genera 

 like Saprolegnia. 



It will be noted that for taxonomic consideration the body pre^dously 

 termed a "presporangium" has been regarded as closely analogous to a 

 sporangium. Some may prefer to discard the prefix and apply the term 

 "sporangium" to the portion of the hypha cut off for purposes of spore 

 production, giving another name to the thin-walled organ in which the 

 spores arise. It has seemed to the author, however, that the name "spo- 

 rangium" should be applied to the organ in which the spores are differ- 

 entiated, and that the term "presporangium," while distinctive, is at the 

 same time clear and accurate, conveying a true idea of the function of the 

 body to which it has been applied. 



In selecting a name for the fungus an effort has been made to choose one 

 which is descriptive of some distinctive character. From the fact that 

 the sporangiiun flows out from the presporangium and that its wall is so 

 delicate as to be almost invisible, the name " Rheosporangizim aphanider- 

 matiis" has been chosen. Its technical description is as follows: 



